The present invention relates to a high-density and large-capacity storage drive and, more particularly, to a storage drive capable of permitting fast writes or reads. Fast writes and reads are permitted even where the storage drive is simultaneously accessed by a plurality of users.
Storage drives of the prior art have typically had low recording densities which have rendered large capacities difficult to realize, even in such cases where high speed access is possible, such as in magnetic disk drives. Conversely, storage drives using magnetic tapes or optical disks arrayed in a "juke box" form provide high capacity, but have a low throughput given their extremely slow access periods. Earlier technology therefore renders it difficult to allow for concurrent access to a mass storage medium from a plurality of associated user terminals.
In earlier systems, large capacity and high-speed access was typically realized by using a magnetic disk as a buffer (or cache) of a magnetic tape library or an optical disk library. Where a certain data record is accessed, according to this method, its neighboring data is also copied from the magnetic or optical disk into the buffering magnetic disk. In this way, data written in a physically near address, having a high probability of being accessed within a concentrated time, can be quickly accessed.
In the technology thus far described, data to be accessed is not originally present on the magnetic disk. Accordingly, a target magnetic tape or optical disk has to be set forth in the drive from the magnetic tape or optical disk library so that the data may be loaded. Such loading often takes several seconds. As a result, in the event that the file device is shared among a plurality of terminals, and in cases wherein continued accesses to data not present on the magnetic buffering disk are demanded, there arises a problem that the access requests are accumulated. This situation invites a state in which a system is incapable of performing the desired transactions.
Use of hybridized storage media raises another problem given that such a storage drive is costly.
The subject invention solves the above referred problems, and others, and provides a single medium mass-storage system which is capable of providing fast and efficient access to mass storage by a plurality of users.